Scanning-less optical near-field characterization for structured light fields based on nonlinear effects

Conventional methods for near-field characterization have typically relied on the nanoprobe to point-scan the field, rendering the measurements vulnerable to external environmental influences.Here, we study the direct far-field imaging of the near-field polarizations based on the four-wave mixing effect.We construct a simulation model to realize the instantaneous extraction of the near-field distributions of a wide range of structured light fields, such as cylindrical vector vortex beams, plasmonic Weber beams, and topological spin textures, including photonic skyrmions and merons.This method is valuable for the studies on manipulation of structured light fields and light-matter interaction at the micro/nano scales.